Differential cylinder-piston assembly



G. W. MOHM DIFFERENTIAL CYLINDER-PISTON ASSEMBLY Maw w@ 2 Sheets-Sheet l Filed July 22, 1946 5M .Fl

INVENOR ATTORNEY may 2g, WSU G. w. Mom( DIFFERENTIAL CYLINDERJISTON ASSEMBLY 2 Sheets-Sheet 2 Filed July 22, 1946 gm-M BY W7 ATTOR/VE l( Patented May 2, 1950 DIFFERENTIAL CYLINDER-PISTON ASSEMBLY George W. Mork. South Milwaukee, Wis.. assignor to Bucyrus-Erie Company, South Milwaukee, Wis., a corporation of Delaware Application July 22, 194s, serial No. 685,306

(ci. 12g- 38) 14 Claims. l

My invention relates to new and useful improvements in differential cylinder-piston assemblies.

The principal object of my invention is to devise a double-acting cylinder-piston assembly, in which the action in each direction will be characterized by a slow-speed high-force motion during the first part of the travel, and then a highspeed low-force motion during at least most of the rest of the travel,

In addition to my principal object, above stated, I have worked out a number of novel and useful details, which will be readily evident as the description progresses.

My invention consists in the novel parts and in the combination and arrangement thereof, which are defined in the appended claims, and of which one embodiment is exemplified in the accompanying drawings, which are hereinafter particularly described and explained.

Throughout the description the same reference number is applied to the same member or to similar members.

Each of the figures constitutes a longitudinal section of my device. In these gures, the cylinder, the auxiliary cylinder-head, and the rods which support it from the cylinder, are fixed; and the hollow piston and its rod are moveable.

Figure l shows the principal variant of my invention, with the hollow piston in its lowest position.

Figure 2 shows this variant, with the hollow piston in an intermediate position.

Figure 3 shows this variant, with the hollow piston in its highest position.

Figure 4 shows a second variant of my invention, with the hollow piston in its lowest position.

Figure 5 shows a third variant of my invention, with the hollow piston in its lowest position.

Referring now to Figure 1, we see that I4 is a cylinder, having midway between its ends a constriction II, with a rod I2 extending up, and a rod I3 extending down, therefrom. The lower end of rod I3 has a fixed anchorage to the bottom of the inside of outer cylinder I4. The upper end of rod I2 isnt fastened to anything.

There is a hollow piston I5, which has a fluidtight sliding contact with the inside of cylinder I4, with constriction II, and with rods I2 and I3. Extending upwardly from, and integral with, hollow piston I5, there is a piston-rod I6, which extends out through a fluid-tight opening in the upper end of cylinder I4. This piston-rod I6 is hollow and embraces upper rod I2, the upper end of which has a fluid-tight sliding contact Within said piston-rod I5.

There is a fluid port I 'I at the bottom of cylinder I4, and a uid port I8 at the top of said cylinder. Stops I9 prevent the ends of piston I5 from abutting the ends of cylinder I4.

On the inner surface of hollow piston I5 there are lengthwise grooves 20 and 2I. On rod I2 there are lengthwise grooves 22. On rod I3 there are lengthwise grooves 23.

At the bottom of piston-rod IB, where it joins the upper end of piston I5, there are openings 24 into the hollow interior of the piston-rod.

It is important to note that grooves 2|), 2|, 22 and 23, Vare so positioned that neither grooves 20 nor grooves 2| will ever by-pass around constriction II, except when grooves 22 and/or grooves 23 are blocked from by-passing respectively through the upper or lowei ends of the hollow piston I5.

As shown, both ends of each set of grooves 22 and 23 are thus blocked by ending short of the two heads of cylinder I 4, and also by ending short of the constriction I I. But it can be readily seen that my invention would continue to operate, if both sets of grooves 22 and 23 were extended either all the way to the two ends of cylinder I4, or all the way to constriction Il, but not both. The effect of these changes will be explained later herein.

A single cylinder-piston assembly may he generically defined as comprising two relativelymoveable parts, namely: a chamber, called a cylinder, although it need not be cylindrical in shape; and a cross-sectional closure for the cy1in, der, called a piston having some area of contact completely around some part of the inner surface of the cylinder in all active positions of the assembly. Motion of the piston with respect to the cylinder is effected by difference in total pressure-force to one side of, and to the other side of, this area of contact.

By the same token, it will be seen that the double cylinder-piston assembly of my invention comprises, in effect, two such pistons, operating in two such cylinders, and moving a common plston-rod. When moving upwardly, the lower end of hollow piston I5 constitutes my main piston, annular in shape, and operating in an annular main cylinder the walls of which are the inner surface of cylinder I4 and the outer surface of rod I3. When moving downwardly, the upper end of hollow piston I5 constitutes my main piston, annular in shape, and operating in an annular main cylinder, the walls of which are the inner surface of cylinder I4 and the outer surface of cylinder I4 and the outer surface of rod I2. When moving in either direction, the wall of hollow piston I constitutes my auxiliary piston, annular in shape, and operating in an annular auxiliary cylinder, the walls of which are the inner surface of cylinder I4 and the outer surface of constriction II.

In view of the foregoing analysis, some of my claims, instead of describing my invention In terms of a hollow piston, having sliding contact with the inner surface of a cylinder, a constricting means, and rods attached to the constricting means, will describe my invention generically in terms of two pistons and two cylinders.

It will be noted that my auxiliary piston, and its cooperating auxiliary cylinder, have a smaller eiective pressure-area than that of my main piston and main cylinder.

When my invention is viewed as two cylinderpiston assemblies, the two pistons being operatively connected so as to actuate Vone common piston-rod, it will be seen that it is necessary, whenever one piston is to be activated and the other one not, that the pressure-fluid must bypass the area of contact between the inactive piston and its cylinder, but must not bypass the area of contact between the active piston and its cylinder.

At the top of piston-rod It there is an opening to the atmosphere, to prevent the building up of pressure or vacuum in the upper end of the hollow interior of said piston-rod i6.

Work to be actuated by my assembly can be attached to said piston-rod IIS, as at 26.

The operation of my cylinder-piston assembly is as follows.

Assume the apparatus to be in the position shown in Figure l. Pressure fluid is admitted, through port Il, into the lower end of the interior of cylinder I4, just below hollow piston I5. There the fluid sets up a pressure against the whole cross-sectional area of the lower end of piston I5, le'ss the cross-sectional area of rod I3. Under the influence of this pressure, piston I5, and its piston-rod I6, move upwardly slowly with great force.

Meanwhile the pressures in the hollow inside of piston I5, above and below constriction II, are equalized through grooves il on the inner surface of the upper end of hollow piston I5. Exhaust from the upper end of cylinder I4 passes out through fluid port I8 at the top thereof.

Turn now to Figure 2. When piston I5 has reached the position shown in this gure, it uncovers grooves 23 in piston-rod I3. Fluid is now free to by-pass the lower end of piston I5, through these grooves, into the hollow interior of said piston. The effective pressure-area accordingly now becomes merely the cross-sectional area of the exterior of piston I5, less the crosssectional area of constriction I I. This effective pressure-area is considerably less than the former pressure-area: thus, from then on, piston I5 and its piston-rod I6 move upwardly considerably faster, and with considerably less force than in the first portion of their travel.

Meanwhile the pressures inside the upper end of cylinder I4, and inside the upper end of hollow piston I5, are equalized through grooves 22 in rod I2 and openings 24 in the lower end of piston. rod I 6. The thus equalized exhaust passes out through iiuid port I8 at the top of the cylinder.

This high-speed low-force travel continues until the piston I 5 reaches the position shown in Figure 3. From then on, the iiuid can by-pass constriction II, but can no longer by-pass the lower end of piston I5 into the interior thereof.

with the result that the initial speed-force ratio is restored. Pressures inside hollow piston Il, above and below constriction II, are equallzed through grooves 20.

The reverse motion is similar, initial and final pressure being against the upper instead of the lower end of piston I5. Fluid under pressure is admitted, through port IB, into the upper end of the interior of cylinder I5, and the exhaust from the lower end thereof passes out through port I1.

As before, the travel is slow and forceful at the beginning and end of the travel, and is fast and less forceful for the travel in between, which is the greater portion of the travel.

By having rods I2 and I3 differ in diameter, and/or by having piston-rod. I6 of appreciable thickness we can arrange to have one, two, or all of the three-speed-force ratios during travel in one direction differ from the corresponding ratios during travel in the other direction.

Turning now to the variant of Figure 4, we see that it is identical to Figure l, except that now grooves 22a extend clear to the top of rod I2, and grooves 23a extend clear to the bottom of rod I3.

Turning now to the variant of Figure 5, we see that it is identical to Figure l. except that now grooves 22h and 23h all extend clear to constriction II.

Each of these two variants can be readily seen to have exactly the same cycle of operations as the variant of Figures 1. 2 and 3.

Having now described and illustrated three forms of my invention, I wish it to be understood that my invention is not to be limited to the specic form or arrangement of parts herein described and shown.

I claim:

1. In a cylinder-piston assembly, the combination of: a cylinder; a constriction within the cylinders; two rods, attached to the constriction, and projecting respectively in opposite directions therefrom, the first of these rods being anchored to the cylinder; a hollow piston, having outwardly a close sliding contact with the interior of the cylinder, and having inwardly a close sliding contact with the constriction, and having at its respective ends a close sliding contact with the two rods; a hollow piston-rod, attached to one end of the piston, and having inwardly a close sliding contact with the second of the two rods, and having outwardly a close sliding contact with the second end of the cylinder; means for alternatively admitting pressure fluid to one or the other end of the cylinder, and for simultaneously permitting exhaust from the opposite end of the cylinder; means for automatically bypassing fluid, past the constriction, from one end of the interior of the hollow piston to the other, whenever either end of said piston is near the corresponding end of the cylinder; and means for automatically by-passing fluid, past each end of the hollow piston, from the interior thereof, to the interior of the cylinder, in intermediate positions.

2. In a cylinder-piston assembly, the combination of: a cylinder; a constriction within the cylinder; two rods, attached to the constriction, and projecting respectively in opposite directions therefrom, the first of these rods being anchored to the cylinder; a hollow piston, having outwardly a close sliding contact with the interior of the cylinder, and having inwardly a close sliding contact with the constriction, and having at its respective ends a close sliding contact with the two rods; means for transmitting relative motion of the piston, with respect to the cylinder, to outside the cylinder; means for alternatively admitting pressure fluid to one or the other end of the cylinder, and for simultaneously permitting exhaust from the opposite end of the cylinder; means for automatically by-passing uld, past the piston, from one end of the interior of the piston to the other, whenever either end of the piston is near the corresponding end of the cylinder; and means for automatically by-passing uid, past each end of the piston, from the interior of the piston to the interior of the cylinder, in intermediate positions.

3. A cylinder-piston assembly, according to claim 2, further characterized by the fact that the flrst by-pass means comprises at least one longitudinal groove in the interior surface of the hollow piston, which groove is uncoverable by relative motion of said piston and the constriction.

l. A cylinder-piston assembly, according to claim 2, further characterized by the fact that the second by-pass means comprises at least one longitudinal groove on the surface of one of the rods, which groove is uncoverable by relative mo- .tion of the piston and the cylinder.

5. A cylinder-piston assembly, according to claim 2, further characterized by the fact that one or another of the by-pass means is always blocked between the two ends of the interior of the cylinder.

6. A cylinder-piston assembly, according to claim 2, further characterized by the fact that the first by-pass means consists of at least one longitudinal groove in the interior Vsurface of each end of the hollow piston; and that the secand lay-pass means consists of at least one longitudlnal groove in the surface of each rod; and that one or another of the by-pass means is a1- ways blocked between the two ends of the interior of the cylinder.

'l'. A cylinder-piston assembly, according to claim 2, further characterized by the fact that the iirst by-pass means consists of at least one longitudinal groove in the interior surface of each. endl of the hollow piston: and that the second by-pass means consists of at least one longitudinal groove in the surface of each rod; and that, whenever the grooves ineither rod are open between the interior of the. piston and the interior of the cylinder, the grooves in the ophesite end oi the piston will not by-pam the constrichon.

il. A cylinder-piston assembly, according to claim 2, further characterized by the- @et that the rst by-pass means consists of at least one longitudinal groove in the interior surface of each end of the hollow piston; and that the second lay-pass means consists of at least one lonaitiidinal groove in the exterior surface of each rod; and that, whenever the grooves in either wd of the piston are open to by-pass the constriction, the grooves in the opposite rod will not by-pass the end of the piston.

9. A cylinder-piston assembly, according to claim 2, further characterized by the fact that,

5 whenever either by-pass means between the interior of the hollow piston and the interior of the cylinder is open, the by-pass means around the constriction will be closed.

10. A cylinder-piston assembly, according to l0 claim 2, further characterized by the fact that,

whenever either lby-pass means around the constriction is open, the opposite by-pass means between the interior of the piston and the interior of the cylinder will be closed.

l 11. In a cylinder-piston assembly the combination of: a main cylinder and a piston therefor, having a relatively large eiective pressure area; an auxiliary cylinder and a piston therefor, having a relatively small effective pressure area; a piston rod, operatively connected to both pistons; and a system of uid conduits providing a bypass past the area of contact between the main piston and its cylinder, and a bypass past the area of contact between the auxiliary piston and its cylinder, these bypasses being opened and closed by the relative motions of the pistons and cylinders, and being so positioned that whenever one bypass is open the other bypassisclosed.

12. A cylinder-piston assembly, according to claim 11, further characterized by the fact that the bypass past the area of contact between the main piston and its cylinder comprises at least one longitudinal groove in the wall of the main cylinder, which groove is uncoverable by re1- ative motion of the main piston and the main cylinder.

13. A cylinder-piston assembly, according to claim 12, further characterized by the fact that the bypass past the area of contact between the auxiliary piston and its cylinder comprises at least one longitudinal groove in the auxiliary piston, which groove is uncoverable by relative motion of the auxiliary piston and the auxiliary cylinder.

14. A cylinder-piston assembly, according to claim 11, further characterized by the fact that the bypass past the area of contact between the auxiliary piston and its cylinder comprises at least one longitudinal groove in the auxiliary piston, which groove is uncoverable by relative motion of the auxiliary piston and the auxiliary cylinder.

GEORGE W. MORE.

REFERENCES CITED The following references are of record in the die ol this patent:

2,023,842 Kingsbury Dec. lll, 1935 

